Tanning process



United States Patent fiicc 3,345,323 Patented Oct. 10, 1967 ABSTRACT OF THE DISCLOSURE Compositions and process employing those compositions in the tanning of animal skins, the composition bination with dolomite or a mixture of dolomite and comprising certain inorganic chrome tanning salts in cornbination with dolomite or a mixture of dolomite and other neutralizing agents.

This invention relates, in general, to a new and improved tanning process, i.e., a process for treating animal hides and skins so as to reduce or prevent their digestion by the many proteolytic bacteria which are present when the skin or hide is flayed. More particularly, the invention provides an improved process of the general class described which utilizes chromic salts, and preferably chromic sulphates, in combination with dolomitic materials as an acid-binder.

In general, light-weight skins, such as those from small animals of the type of goats or sheep, or from immature animals such as calves, are referred to in the leather industry as skins, whereas heavy-weight skins derived from large, mature animals such as steers, cows, or buffalo are termed hides. As used throughout the present specification and appended claims, however, the term skin is employed in its inclusive sense and refers to both light and heavy skins.

Additionally, within the scope of the present invention, the term dolomite denotes the mineral double salt CaCO 'MgCO which contains from 20 to 40 percent, and preferably from 25 to 35 percent, of C210, and from to 25 percent, or preferably from 16 to 24 percent, of MgO, either when employed alone or in combination with other acid-binding substances in the manner explained hereinafter.

In the tanning of animal skins with chromic salts, sodium carbonate and sodium bicarbonate have customarily been employed heretofore as the acid-binding substances, and these are immediately neutralized by the acids formed from the chromic salts employed, via a hydrolysis mechanism. Tanning under these conditions involves the risk that at the points where such conventional acid-binding agents are introduced into the tanning liquor, chromium compounds may be formed which possess too high a basicity, resulting in participates which cannot be redissolved. Admittedly, attempts have been made to obviate this specific disadvantage by adding the required amount of such conventional acid-binding substances to the tanning liquors in the dissolved form during the tanning process and over the course of a prolonged period of time, either step-wise or continuously, but rather special addition schedules must be worked-out and faithfully followed in order to achieve the desired endpurpose under these circumstances.

The present invention is based, at least in part, on the discovery that the use of dolomite, as per the compositions stated hereinbefore obviate the disadvantages described above. Thus, dolomite reacts with the acid liberated by hydrolysis from the chromic salts relatively slowly during the course of several hours. Tanning with chromic salts is thereby substantially simplified through use of the dolomite acid-binder pursuant to the process of the invention.

Inasmuch as the acid liberated from the chromium compounds is bound by the dolomite very slowly, the precise amount of dolomite required for neutralization can be added immediately at the start of the tanning process in a single portion, since no chromium compounds can be formed with these circumstances which possess too high a basicity and tend to precipitate. Furthermore, even if the chromic salts are adjusted to high final basicity in order to make optimum use of the chromium, the use of dolomite as the acid-neutralizing agent permits one to produce leather of outstanding quality in an otherwise reliably controlled tanning process.

As indicated above, dolomite suitable for use in the process of the invention contains the above-stated amounts of calcium oxide and magnesium oxide in the form of calcium carbonate and magnesium carbonate. Dolomites of this composition have been described, inter alia, in Ullmanns Encyclopadie der technischen Chemie, 3rd edition, 12th volume, Verlag Urban and Schwarzen'ber-g, Munich/ Berlin (1960), page 77, and in Handbuch der Mineralogie, by C. Hintze, Verlag Walter de Gruyter and Co., Berlin (1930), volume 1, first half of section 3, pages 3342 to 3350.

A substantial variety of known salts are suitable for use as chromic salts in tanning, especially chromic sulphates, basic chromic sulphates, masked chromic salts, such as acetate-masked chromic sulphate, and mixtures of basic chromic sulphates and non-tanning inorganic salts, such as sodium sulphate, and also reaction products of compounds of 6-valent chromium with reducing agents, as described inter alia, in Ullmanns Encyclopadie der technische-n Chemie, 3rd edition, 11th volume, pages 604607, and in The Chemistry and Technology of Leather, Reinhold Publishing Company, New York (1958), vol. 2, pages 254 to 259.

As indicated hereinbefore, the dolomite can be used in the tanning process of the invention with the chromic salts, either by itself, or in admixture with conventional acid-neutralizing agents such as sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, calcium carbonate and sodium sulphite. By employing mixtures of the dolomite with such other conventional neutralizing agents, and especially the above enumerated conventional agents, an acceleration of the acid-binding mechanism is generally achieved without having to encounter the aforedescribed undesirable effects resulting from the sole use of the conventional neutralizing agents. The proportion of dolomite present in the total amount of such mixed neutralizing agents must be at least 10%, however, in order to achieve the desired etfects of the invention.

The dolomite and chromic salts can be added to the tanning liquor separately, or in the form of a mixture, the latter method offering substantial technical advantages from the standpoint of production techniques. In the latter connection, mixtures of chromic salts, especially chromium sulphate, and dolomite, possibly in combination with other conventional neutralizing agents, are products of commerce and can generally be made available to the tanner as ready-made compositions. Thus, the separate addition of an acid-binding substance to the chrome tanning bath is no longer necessary in accordance with the practices of our invention.

The ratio of chromic salts, especially chromic sulphates, to dolomite preferably ranges from 6-130 parts by weight of dolomite per parts by weight of Cr O the Cr O being present as a chromic salt, especially chromic sulphate, basic chromic sulphate, masked chromic sulphates, masked basic chromium-(HI)-sulphates, and the like. The exact amount of dolomite employed in accordance with the process of the invention depends on the basicity of the chromic salts employed, upon the basicity to which the chromic salts are to be adjusted during tanning, and upon the amount of further acid-binding substances which may be added to the mixture or during the tanning process.

Significantly, the technical advantages achieved by the process of the invention through use of dolomite of the stated composition as the acid-neutralizing agent are quite suprising. Thus, it has been found, for example, that these advantages are not attained if, in place of dolomite, a mixture of the magnesium carbonate and calcium carbonate in amounts corresponding to the dolomite is employed. That is to say, when using direct mixtures of magnesium carbonate and calcium carbonate, and also when using one or the other of these carbonates alone/the acids liberated from the chromic salts by hydrolysis are neutralized immediately, thereby leading to the same disadvantages as described above.

It is believed that the invention may be best understood by reference to the following specific examples illustrating the application of the foregoing principles and procedures'to the tanning of typical animal skins (the parts being parts by weight):

Example I One hundred (100) parts of powdered chromic sulphate with a content of 26 percent of Cr O 27 percent of S0 and 23 percent of Na SO and 16 parts of ground dolomite with a content of 30.6 percent of CaO and 21.5 percent of MgO were admixed with one-another. One hundred (100) parts of a pickled calf pelt were then drummed with 13 parts of this mixture and 70 parts of water in a drum for 8 hours. The initial temperature reached 20 C., whereas the final temperature was 40 C. The resulting leather was found to be resistant to boiling water.

Example II One hundred (100) parts of the powdered chromic sulphate described in Example I were mixed with 18 parts of ground dolomite containing 27.4 percent of CaO and 23.4 percent of MgO. One hundred (100) parts of a pickled calf pelt were then drummed with 13 parts of this mixture and 70 parts of water in a drum for 8 hours. The initial temperature was 20 C., and the final temperature 40 C. The leather thus obtained w as also found to be resistant to boiling water.

Example III One hundred (100) parts of the powdered chromic sulphate described in Example I were mixed with 17 parts of ground dolonite containing 34.1 percent of CaO and 17.3 percent of MgO. One hundred (100) parts of a pickled calf pelt were then drummed with 13 parts of this mixture and .70 parts of water in a drum for 8 hours. The initial temperature was 20 C., and the final temperature was 40 C. The leather thus produced was found to be resistant to boiling water.

Example IV One hundred (100) parts of the powdered chromic sulphate described in Example I were mixed with 16 parts of ground dolomite containing 32.6 percent of CaO and 18.6 percent of MgO. One hundred (100) parts of a pickled calf pelt were then drummed with 13 parts of this mixture and 70 parts of water in a drum for 8 hours. The initial temperature was 20 C., and' the final temperature was 40 C. The leather thus produced was found to be resistant toboiling water.

'4 Example V One hundred parts of powdered chromic sulphate with a content of 24.5 percent of Cr O 1.5 percent of A1 0 24.9 percent of S0 and 27 percent of Na SO and 14 parts of ground dolomite containing 30.6 percent of CaO and 21.5 percent of MgO were admixed with oneanother. One hundred (100) parts of a pickled calf pelt were then drummed with 12 parts of this mixture and 70 parts of water in a drum for 8 hours. The initial temperature was 20 C., and the final temperature 40 C. The leather thus produced was found to be resistant to boiling water.

Example VI One hundred (100) parts of powdered chromic sulphate with a content of 26.6 percent of Cr O 21 percent of S0 and 30 percent of Na SO and 8 parts of ground.

dolomite containing 30.6 percent of CaO and 21.5 percent of MgO were admixed with one-another. One hundred (100) parts of a pickled calf pelt were then drummed with 13 parts of this mixture and 70 parts of water in a drum for 8 hours. The initial temperature was 20 C., and the final temperature 40 C. The leather thus produced was found to be resistant to boiling water.

Example VII One hundred (100) parts of a powdered chromic I One hundred (100) parts of an acetate group-containing chromic sulphate having a content of 26.3 percent of Cr O 26.5 percent of S0 23.1 percent of Na SO and 5 percent of CH COOH, prepared pursuant to the process of Belgian patent specification No. 609,653, were admixed with 24 parts of ground dolomite containing 30.6 percent of CaO and 21.5 percent of MgO. One hundred 100) parts of a pickled calf pelt were drummed with 10 parts of this mixture in a drum for 7 hours. The initial temperature was 20 C., and the final temperature 40 C. The leather thus produced was found to be resistant to boiling water.

Example IX One hundred (100) parts of the powdered chromic sulphate described in Example I were mixed with 8 parts of ground dolomite containing 30.6 percent of CaO and 21.5 percent of MgO, and with 14 parts of sodium car- 'bonate. One hundred (100) parts of a pickled calf pelt were then drummed with 14 parts of this mixture and 70 parts of water in a drum for 6 hours. The initial temperature was 20 C., and the final temperature 40 C. The leather thus produced was found to be resistant to boiling water. 7

Example X One hundred (100) parts of the powdered chromic sulphate described in Example I were mixed with 12 parts of ground dolomite containing 34.1 percent of C30 and 17.3 percent of MgO, and with 5 parts of sodium carbonate. One hundred (100) parts of a pickled calf pelt were then drummed with 12 parts of this mixture and 70 parts of water in a drum for 6 hours. The initial temperature was 20 C., and the final temperature 40 C. The leather thus produced'was found to be resistant to boiling water.

Example XI One hundred (100) parts of the powdered chromic sulphate described in Example I were mixed with 8 parts of ground dolomite containing 27.4 percent of C210 and 23.4 percent of MgO, and with 9 parts of calcium carbonate. One hundred (100) parts of a pickled calf pelt were then drummed with 12 parts of this mixture and 70 parts of water in a drum for 6 hours. The initial temperature was 20 C., and the final temperature 40 C. The leather thus produced was found to be resistant to boiling water.

Example XII One hundred (100) parts of the powdered chromic sulphate described in Example I were mixed with 12 parts of ground dolomite containing 32.6 percent of CaO and 18.6 percent of MgO, and with 12 parts of sodium sulphite. One hundred 100) parts of a pickled calf pelt were then drummed with 12 parts of this mixture and 70 parts of water in a drum for 7 hours. The initial temperature was 20 C., and the final temperature 40 C. The leather thus produced was found to be resistant to boiling water.

Example XIII One hundred 100) parts of a pickled calf pelt were drummed in a drum for 8 hours with 16 parts of a chromic sulphate solution (containing 18 percent of Cr O 18.9 percent of S0 and 23 percent of Na SO 2 parts of dolomite (containing 30.6 percent of CaO and 21.5 percent of MgO), and 50 parts of Water. The initial temperature was 20 C., and the final temperature 40 C. The leather thus produced was found to be resistant to boiling water.

Example XIV One hundred 100) parts of a pickled calf pelt were drummed in a drum for 8 hours with a solution of 20 parts of potassium chromium alum in 70 parts of water with the addition of 3.3 parts of dolomite containin 32.6 percent of CaO and 18.6 percent of MgO. The initial temperature was 20 C., and the final temperature was 40 C. The leather thus produced was found to be resistant to boiling water.

As will be readily appreciated by those skilled in the art, in place of the calf pelts utilized in the foregoing examples, any other animal pelt, such as cow pelts, goat pelts or sheep pelts, for example, may be utilized in the tanning process of the invention, and leathers resistant to boiling water are thus obtained. Additionally, following application of the tanning process of the invention, the resulting leathers can be finished in accordance with conventional practices.

What is claimed is:

1. In a process for tanning animal skins involving the use of inorganic chrome tanning salts and acid-binding agents, the improvement that comprises employing as said acid-binding agent, a member selected from the group consisting of dolomite, and (at least ten ercent (10%) calculated on the total amount of neutralizing agents of dolomite in combination with at least one) mixtures of dolomite and one or more other neutralizing agents selected from the group consisting of sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, calcium carbonate and sodium sulphite in which dolomite constitutes at least 10% by weight of said mixture.

2. The improved process as defined in claim 1, wherein the inorganic chrome tanning salts consists of at least one member selected from the group consisting of unmasked basic and nonbasic chromic sulphates, masked basic and nonbasic chromic salts, and mixtures of said chromic sulphates or said chromic salts with non-tanning neutral inorganic salts.

3. The process as claimed in claim 1 wherein said inorganic chrome tanning salt is applied in admixture with said acid-binding agent.

4. The process as claimed in claim 1, wherein said dolomite consists of the mineral double salt CaCO MgCO and has a content of from 20 to 40 percent of C210, and from 10 to 25 percent of MgO.

5. The process as claimed in claim 1, wherein said dolomite consists of the mineral double salt CaCO MgCO and has a content of from 25 to 35 from 16 to 24 percent of MgO.

6. A composition for use in the tanning of animal skins which comprises (1) at least one inorganic trivalent chrome tanning salt selected from the group consisting of unmasked basic and nonbasic chromic sulphates, masked basic and non-basic chromic salts, mixtures of said chromic sulphates or said chromic salts with non-tanning neutral inorganic salts, and (2) dolomite or a mixture of dolomite and one or more other neutralizing agents selected from the group consisting of sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, calcium carbonate and sodium sulphite in which dolomite constitutes at least 10% by weight of said mixture.

7. The composition as claimed in claim 6, wherein there is employed from 6 to 130 parts by weight of dolomite for every parts by weight of Cr O present in the chrome tanning salts employed.

percent of 0210, and

References Cited Chemical Abstracts, Vol. 54, 1960, col. 12507 and 12508.

DONALD LEVY, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,346,323 October 10, 1967 Heinrich Spahrkas et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 17, strike out "bination with dolomite or a mixture of dolomite and"; column 2, line 10, for "with" read under column 3, line 57, for "dolomite" read dolomite column 4, line 28, for "reduced" read reduction column 6, lines 2 to 4, strike out "(at least ten percent (10%) calculated on the total amount of neutralizing agents of dolomite in combination with at least one)"; same column 6, line 12, for "consists" read consist Signed and sealed this 19th day of November 1968. SEAL) vttest:

iward M. Fletcher, Jr. EDWARD J. BRENNER [testing Officer Commissioner of Patents 

1. IN A PROCESS FOR TANNING ANIMAL SKINS INVOLVING THE USE OF INORGANIC CHROME TANNING SALTS AND ACID-BINDING AGENTS, THE IMPROVEMENT THAT COMPRISES EMPLOYING AS SAID ACID-BINDING AGENT, A MEMBER SELECTED FROM THE GROUP CONSISTING OF DOLOMITE, AND (AT LEAST TEN PERCENT (10%) CALCULATED ON THE TOTAL AMOUNT OF NEUTRALIZING AGENTS OF DOLOMITE IN COMBINATION WITH AT LEAST ONE) MIXTURES OF DOLOMITE AND ONE OR MORE OTHER NEUTRALIZING AGENTS SELECTED FROM THE GROUP CONSISTING OF SODIUM CARBONATE, POTASSIUM CARBONATE, SODIUM BICARBONATE, POTASSIUM BICARBONATE, CALCIUM CARBONATE AND SODIUM SULPHITE IN WHICH DOLOMITE CONSTITUTES AT LEAST 10% BY WEIGHT OF SAID MIXTURE. 